Memory devices are typically provided as internal, semiconductor, integrated circuits in computers or other electronic devices. There are many different types of memory, including random-access memory (RAM), read only memory (ROM), dynamic random access memory (DRAM), synchronous dynamic random access memory (SDRAM), resistive memory (e.g., RRAM), and Flash memory, among others.
Memory devices can be utilized as volatile and non-volatile data storage for a wide range of electronic applications. Volatile memory may require power to maintain its data, whereas non-volatile memory may provide persistent data by retaining stored data when not powered. Flash memory, which is just one type of non-volatile memory, can use a one-transistor memory cells that allow for high memory densities, high reliability, and low power consumption. Non-volatile memory may be used in, for example, personal computers, portable memory sticks, solid state drives (SSDs), digital cameras, cellular telephones, portable music players such as MP3 players, movie players, and other electronic devices.
Memory devices can have arrays of memory cells. Memory arrays can include groups of memory cells, such as blocks, sub-blocks, strings, etc. In some examples, a memory array can be a stacked memory array that can be referred to as a three-dimensional (3D) memory array. The memory cells at a common location (e.g., at a common vertical level) in a stacked memory array, for example, may form a tier of memory cells. The memory cells in each tier can be commonly coupled to a common access line, such as a word line. In some examples, a group of memory cells can include memory cells from different tiers coupled in series to form a string of series coupled memory cells (e.g., a NAND string) between a select transistor coupled to a source and a select transistor coupled to a data line, such as a bit line.
In some examples, the formation of stacked memory arrays can include a replacement gate process. After semiconductor structures (e.g., semiconductor pillars) are formed through a stack of alternating dielectrics, a replacement gate process can be used to remove dielectrics from the stack at levels at which memory cells are to be formed adjacent to the semiconductor structures and to form conductive access lines (e.g., metal access lines) in place of the removed dielectrics. In various examples, an opening (e.g., a slot or slit) can be formed through the stack to provide access to the various levels in the stack in order to remove selected dielectric material layers (e.g., via an etchant) and replace them with levels of conductive material (e.g., a metal) that can serve as the access lines.